The invention is in the field of x-ray machines, such as those used for medical diagnostic x-ray imaging. An important aspect pertains to automatically selecting technic factors in response to an operator-selected mAs setting and automatically supplying the x-ray tube with power at a KV selected by an operator setting, in particular by automatically delivering the correct voltage to the primary winding of the HT transformer as a result of a binary sequence selection of a series connection of relay-controlled secondary windings of a power transformer.
A system for automatic selection of technic factors such as KV, mA and exposure time is disclosed in commonly owned U.S. Pat. Nos. 4,597,094 and 4,403,337, the disclosure of which is hereby incorporated by reference as though fully set forth herein. Equipment embodying certain aspects of the inventions disclosed in said patents is commercially available from the common assignee under the tradename Bennett AUTO-TECH System, and can be used in conjunction with x-ray machines available from the same assignee under the designations P-325, CM-425 and P-625. In one system disclosed in said patents and literature on said Auto-Tech System, there is an automatic selection of the technic factors on the basis of (i) an automatic determination of the anatomical thickness (of the body part to be x-rayed) through the use of a non-contact ranging system (such as a sonic or an infrared beam ranging system), (ii) if needed, a push-button identification of the body region to be x-rayed (e.g., skull, thorax, extremity, etc.), and (iii) a push-button selection of the anatomical part (e.g., hand, wrist, forearm, elbow, humerus, tibia, etc.). The result is an automatic selection of KV, mA and mAs for the particular exposure, to thereby ensure consistent high quality images and eliminate the need for the operator to use calipers and refer to technic charts. Such auto-selection is implemented in the equipment identified in the brochure of the assignee entitled "Bennett AUTO-TECH System," which is hereby incorporated by reference herein.
In another system, which is disclosed in said parent application and which forms a part of the invention claimed in this application, the x-ray machine has an otherwise conventional control panel with several discrete timer selections, mA stations and mAs settings. However, unlike conventional control panels, the system also includes a processor responsive to the selection of an mAs setting to automatically select and display the combination of a timer selection and an mA station which best approximates the selected mAs setting. The KV is also automatically selected.
Once the technic factors are selected, it is necessary to ensure that the x-ray tube is operated in accordance with the selection. One prior art way of doing this is to use a transformer with a movable tap on the secondary side, and to manually adjust the tap position in order to deliver power the the x-ray tube at the required KV. One disadvantage of this is the need for manual adjustment and the complications of a movable transformer tap, and the need to have the operator rely on an accurate meter which would show the level of the manually selected KV.
In contrast, this invention in response to an operator-selected KVP setting automatically supplies the x-ray tube with power at the correct KV, by using a transformer which does not have movable taps. The transformer uses a set of secondary windings which can be selectively included in a series circuit (and, if needed, added to or subtracted from line voltage) by respective relays controlled by a binary sequence from a microcomputer. For example, six secondary windings can be used, the first at 1.9V output, the second at 3.8V, the third at 7.6V, etc., assuming nominal line voltage at the primary winding. (In fact, in the preferred embodiment there is a slight deviation from a perfect binary sequence, as the fourth winding is at 15.3 rather than at 15.2V.) Thus, for a line voltage of 220 VAC to the primary winding, any collective secondary voltage in the range of about 90 to 340 VAC can be obtained, in steps of about 1.9 VAC, by adding up the output voltage of secondary windings (and, if needed, by adding or subtracting the result from the 220 VAC line voltage). The resulting collective secondary voltage can be supplied to a second transformer having a fixed turn ratio, whose secondary winding powers the x-ray source at a KV determined by the collective secondary voltage of the first transformer. Provisions are made for calibration to account for variations in the line voltage.
In said earlier patents the technic factors are selected on the basis of an automatic measurement of the anatomical thickness of the body part to be imaged, using for the purpose a ranging transducer relying on a beam of acoustic or light energy. A system relying on such automatic measurement of anatomical thickness for fully automatic selection of technic factors, and on a binary sequence to select a series circuit of relay-controlled secondary windings in the manner disclosed in detail below, was described at a meeting for dealers of the assignee of this application and was on sale in this country in 1986, more than a year before the filing date of this application. However, a system using the binary sequence selection of a series circuit of secondary windings in conjunction with operator selection of an mAs setting and thereafter an automatic selection of other technic factors, as described in detail below, has not been described or placed on sale more than a year before the filing date of this application .